The present invention relates to a command issuing apparatus for a high-speed serial interface.
In recent years, IEEE 1394 interfaces have received attention as high-speed serial interfaces for interconnecting audiovisual apparatuses and computers. The IEEE 1394 technology can be used not only for communications between computers through ATAPI (AT Attachment Packet Interface) and SCSI (Small Computer System Interface), which are conventional parallel interfaces, but also for communications between audiovisual apparatuses. This is because IEEE 1394 defines asynchronous communication and isochronous communication.
When computer data is stored in a magnetic disk such as a hard disk or an optical disk such as a DVD-RAM or computer data stored in such a disk is read by a host computer using the IEEE 1394 technology, a control command and data is typically transmitted using asynchronous communication. SBP-2 (Serial Bus Protocol 2), which is a protocol using asynchronous communication, has been generally used for communication between the host computer (initiator) and the hard disk or DVD-RAM (target).
With the commencement of digital broad casting services in Japan, the fusion of audiovisual apparatuses and computers has been accelerated and a hard disk and DVD-RAM have begun to be used as a recording medium for a set top box (STB). Audiovisual data is recorded on these disks in a format that can be handled as a computer file in order to facilitate the management and editing of the data. In such a case, it is required that an SBP-2 initiator capability be provided in the STB, which is an audiovisual apparatus.
Because the dominating apparatuses having the SBP-2 initiator capability have been computers, central processing units (CPUs) offering sufficient speed performance have controlled the transmission and reception of all packets, especially the generation of packets containing operation request blocks (ORBs), in accordance with a program. However, in terms of a cost/performance ratio it is difficult to include a CPU offering sufficient speed performance in an audiovisual apparatus.
In addition, when audiovisual data is recorded or images are reproduced or edited in a target apparatus (such as a hard disk drive or DVD-RAM drive) by an initiator apparatus (STB), the CPU cannot provide sufficient command execution speeds and therefore transmission performance of the target apparatus cannot be fully exploited. Furthermore, required transfer performance of the entire system cannot be achieved.